This application is for a Research Supplement to promote diversity in health related research, specifically to support Dr. Hazeem Okunola in the postdoctoral research phase of his training, with the ultimate goal of his becoming an independent and productive environmental health researcher. In this application 1) The Parent Grant is briefly summarized; 2) Dr. Okunola's proposed activities within the Parent Grant are described, which will enhance the research in the grant while remaining within its approved Specific Aims; and 3) a Training and Mentoring Plan is described, specifically tailored for Dr. Okunola, designed to provide him with the skills that are needed for him to become an independent and productive environmental health researcher. In Aim 1A of the Parent Grant a large prospective cohort study is being undertaken using frozen blood samples from individuals from the Breast Cancer Prospective Family Study Cohort (ProF-SC), to assess the potential association between phenotypically characterized DNA Repair Capacity (DRC) and Breast Cancer (BC) risk. Dr. Okunola will be responsible for two significant enhancements of the current parent grant: 1. Beyond PBMCs: Probing person-to-person variations in DNA repair capacity in PBMC subtypes. In summary, using our current protocols we will not know if inter-individual differences in DNA repair capacity derive uniformly from all the PBMC subtypes or predominantly from specific PBMC subtypes. Dr. Okunola's proposed studies should allow a definitive answer to this question. 2. Looking to the Future: Generating cell lines from blood samples that show either diminished or enhanced DNA repair capacity. Here the goal is for Dr. Okunola to establish immortalized cell lines from PBMC samples from the individuals with the highest / lowest levels of DNA repair capacities. No such set of cell lines defined by anomalous DRC currently exist, and it is anticipated that they will become a valuable resource for future mechanistically based studies, both in our group and worldwide. The key aspect of this Supplement will be training and Mentoring Dr. Okunola to become an independent productive investigator who will make a significant long-term contribution in environmental-health-related biomedical research. The Parent Grant is a highly multidisciplinary project and Dr. Okunola will interact with faculty representing epidemiology, DNA damage / repair, biomarkers, and biostatistical modeling. Dr. Okunola's will participate in a customized structured postdoctoral training program focusing on environmental health policy, professionalism, leadership and management, communication, career management, and responsible conduct of research. It will consist of multiple distinct series and minicourses that together will enable him to gain insights into available career development options, to engage in training / education activities focused on his preferred career track, to adhere to professional ethical codes of conduct, to hone his leadership / managements skills, to optimize his communication skills for academic research positions, and to transition from training to independence.